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Plant Cell. 2014 Sep;26(9):3745-62. doi: 10.1105/tpc.114.130534. Epub 2014 Sep 16.

A root-expressed L-phenylalanine:4-hydroxyphenylpyruvate aminotransferase is required for tropane alkaloid biosynthesis in Atropa belladonna.

Author information

1
Department of Horticulture, Michigan State University, East Lansing, Michigan 48824.
2
Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824.
3
Plant Biology Program and Department of Pharmaceutical Sciences, University of Kentucky, Lexington, Kentucky 40546.
4
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824.
5
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824 Department of Chemistry, Michigan State University, East Lansing, Michigan 48824.
6
Department of Horticulture, Michigan State University, East Lansing, Michigan 48824 barrycs@msu.edu.

Abstract

The tropane alkaloids, hyoscyamine and scopolamine, are medicinal compounds that are the active components of several therapeutics. Hyoscyamine and scopolamine are synthesized in the roots of specific genera of the Solanaceae in a multistep pathway that is only partially elucidated. To facilitate greater understanding of tropane alkaloid biosynthesis, a de novo transcriptome assembly was developed for Deadly Nightshade (Atropa belladonna). Littorine is a key intermediate in hyoscyamine and scopolamine biosynthesis that is produced by the condensation of tropine and phenyllactic acid. Phenyllactic acid is derived from phenylalanine via its transamination to phenylpyruvate, and mining of the transcriptome identified a phylogenetically distinct aromatic amino acid aminotransferase (ArAT), designated Ab-ArAT4, that is coexpressed with known tropane alkaloid biosynthesis genes in the roots of A. belladonna. Silencing of Ab-ArAT4 disrupted synthesis of hyoscyamine and scopolamine through reduction of phenyllactic acid levels. Recombinant Ab-ArAT4 preferentially catalyzes the first step in phenyllactic acid synthesis, the transamination of phenylalanine to phenylpyruvate. However, rather than utilizing the typical keto-acid cosubstrates, 2-oxoglutarate, pyruvate, and oxaloacetate, Ab-ArAT4 possesses strong substrate preference and highest activity with the aromatic keto-acid, 4-hydroxyphenylpyruvate. Thus, Ab-ArAT4 operates at the interface between primary and specialized metabolism, contributing to both tropane alkaloid biosynthesis and the direct conversion of phenylalanine to tyrosine.

PMID:
25228340
PMCID:
PMC4213168
DOI:
10.1105/tpc.114.130534
[Indexed for MEDLINE]
Free PMC Article

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